In general, a specific type of sampler has been widely used to explore for a manganese nodule.
Since the manganese nodules are distributed over a wide area of a deep sea floor, a free-fall grab (FFG) is used to reduce the time taken to collect a sample, and to accurately conduct a statistical analysis and a sample analysis.
Since the FFG is dropped into sea without any wires connected to a research ship, several FFGs may be simultaneously used at one fixed point. The FFG has a sampling time shorter than that of a box corer (BC).
However, the FFG can only recover the manganese nodules scattered in a surface layer, but cannot collect the manganese nodules mixed with sediment.
Even when collecting manganese nodules on a surface layer, due to an error of a machine operated to recover the manganese nodules through the FFG, manganese nodules having large sizes may be gained. In addition, if a manganese nodule lodges at an edge of a sample collecting net of the FFG, since the net is not fully closed, a small size of a manganese nodule may be lost while the FFG is being recovered to the surface of a sea.
One example of the related art is disclosed in Korean Patent No. 10-1046577 (issued on Jun. 29, 2011). A collecting apparatus disclosed in Korean Patent No. 10-1046577 is capable of sampling each layer of bottom seawater near seabed.
Recently, the BC has been used to reduce the sampling time. Without any disturbance, sediment is collected together with manganese nodules distributed on seabed, so that the manganese nodules in the sediment may be obtained.
Thus, the abundance may be estimated, which is more approximate to the actual abundance than that by the method using the FFG.
However, when samples are collected at the same point by using both devices, it is impossible to collect samples exactly at the same point due to a factor such as an ocean current or a current meteorological state.
Further, the sampling time may be significantly increased.
In addition, the samples collected by both devices cannot be compared with each other and the collecting efficiency of the FFG cannot be measured.